fiery

My Feedback: (2)

My MVVS Boxer twin

AMB

Fiery I never knew they made one, did you put 2- 60 diesel heads on it?? stunning nice bike too, now have her put the engine down and taker her out for dinner cheers martin just did a search on Google nothing came up except the petrol twins

Patxipt

I don't see any engine or BMW bike

Seriously, that's a nice boxer (both of them), factory conversion? We need videos of it running dude![8D]

earlwb

I saw that engine a few times before. I tried to get one a while back but other people wanted it a lot more than I did.
Congrats on your engine.
What are you going to put it in to fly?

fiery

My Feedback: (2)

Thanks for the kind words Gents.

The MVVS 1.20 twin shown by my girlfriend was purchased as a used example from a contributor to a thread about it on the RCU MVVS forum. The earlier twins are 1.20 c.i. displacement, later engines are 1.44 c.i. The later spec. is not what I wanted, as I wanted a simple process for conversion. These engines came with a Walbro carb. As far as I know they were only ever sold with as glow engines. They have been out of production since the mid 2000's, and the factory has advised me they will not be re-manufactured. Used examples come up fairly regularly for sale.

A twin diesel has been something I have wanted to try for some time. They do of course exist, but in my mind I cannot justify the prices paid for a Taplin, or one of the German hand built examples such as an FMO. Even if I was to, parts would also be a concern as I would wish to fly it. As I fly R/C, reliable throttling is also a priority.

I decided an MVVS twin 1.20 diesel would be worth a try. I contacted the MVVS factory in the Czech Republic by email. They were happy to supply me with two diesel heads (spares for the .61 Diesel) and extra head shims at very reasonable cost. The heads are beautifully made. The brass contra sits within an aluminium head button. The 1.20 fortunately utilises the same piston, liner and head of the .61 single. I intend to use the shims so that when tuned the contra will sit flush in the head.

My example of the 1.20 has not yet been fired up by myself. It has only limited running (no more than a few minutes) by the previous owner. The carb was removed as the previous owner over tighted a hold down stud and the broken end is still in the hole. I will need to extract it, and possibly clean up the thread if it has been deformed.

These twin engines have a patchy reputation, seemingly due to the inability of the Walbro carb to supply enough glow fuel for a reliable "fat" tune. The reed valves are also considered by some users to be restrictive. I will seek to run it in as a glow, and then convert to diesel operation. With the diesel needing less fuel, the carb may not need any modification to its jets.

Now that the rain has eased I will work on this project and post again once I have some findings.

Hobbsy

My Feedback: (102)

I always like to explain that when a carb with a demand regulator or a Cline regu;ator is used the carb has no reason to supply fuel much beyond the demand. Several people have let themselves get frustrated when not being able to over richen an engine when equipped with a Cline or IronBay regulator. Not a real concern especially whe its a Diesel.

Derek, do you race that Beemer or is it your daily ride, Thanks Dave

Mine is rapidly approaching 15,000 miles.

pe reivers

Derek,

For diesel operation, get rid of the Walbro carb, and fit a normal 10cc carb. Item # 3219

gmedson

Hi Fiery - Wow! Beautiful Engine! Beautiful Bike! Beautiful Girlfriend! Life is Good...

I have no experience with category no. 3. But when I was much younger I did have a Bultaco dirt bike. Anybody remember the Bultacos, Montessas, and Ossas? OK, then, how about Greeves? Couple of friends had Greeves Motocross bikes. Strange machines...

WRT the MVVS, that is a super neat project! Somewhere along the line, I heard negatives about the 1.20 boxer, but it would be interesting if one would become a good running diesel. What carb do you intend to use? Diesels' need for smaller choke area opens many possibilities. Most any .60-size rc glow carb? I wonder how much reed valve will limit high-end performance. Some big gasoline model engines do use reed valves, though.

Nice to know the MVVS company was responsive to your need for new heads.

Good luck. And keep us posted.

Regards. -Gary

AMB

Derek Just a guess, maybe you could use have a plate machined with a tube to hold the carby Pe suggested. Being a flat flange on the engine should not be a big deal

best to you regards martin

Hobbsy

My Feedback: (102)

Derek, I hope you don't mind us going in this direction a wee bit further, For years Mr. Davis has advised me to lose the Del Lorto carb on my Tartan 1.34, so ironically I did so about 4 days ago. I made an adapter to put a SuperTigre 2300 carb on the 1.34. The Del Lorto is an 8mm carb. It ran very well with the Del Lorto so I don't know what the disadvantage is supposed to be, in fact it ran perfectly. I partially drilled the pulse port through the adapter in case I want to use a Cline regulator in the future.

PS, Gary I rode a MAICO in the mid 70s. I wish I had it now. This is identical to mine but mine was yellow and part of the first run to have a 6 speed tranny.

gkamysz

My Feedback: (19)

Was either the MVVS 120 or 144 twin known for weak crankcases? I seem to remember hearing something about it and knew somebody who had one with a cracked case.

I wouldn't discount the use of a Walbro carb for diesel. It should do fine as long as the carb doesn't get hot enough to boil the ether. However if the stock carb was set up for methanol, it may not be ideal for proper mixture on diesel or gasoline. I ran an OS FS-91 as diesel with a Walbro in some testing.

Hobbsy

My Feedback: (102)

Jim Cline actually had an adapter made that he sold to use a SuperTigre carb for Diesel conversions when he was the Tartan distributor. It really takes more than somebody saying, "it won't work" to make it not work.

gmedson

Hi Fiery - Have you run the dieselized MVVS 1.20 boxer twin yet? -Gary

fiery

My Feedback: (2)

Hi Gary

I have found some great tips from a gent in the US (Bill Vail) who had the late Jim Cline sort his out. A Simple mod on the intake to get the beast running smoothly. I will see if I can find the pics and if I can I will post them back.

I am working on setting up a new carb plinth and re-routing the pressure pulse actuation for the Walbro. Also waiting on Carb hold down studs.

Busy at work right now, but this project will be seen through to the end.

***

Edit - pics are of Bill Vail's modifications, which I will follow. A more advanced (but time and labour intensive) option with the possibility of enhanced performance would be to fabricate a new reed block with a larger aperture for the lean cylinder; or alternatively perhaps with the reed block being moveable so as to be set up slightly "assymetric" (i.e. offset) to the intake downdraught, with the lean running cylinder being more in line with gas flow, thereby being fed more mixture.

If anyone wants to know more, jump to the "MVVS Support" forum, and click on the "MVVS Twins" thread. More details, and running figures (as supplied by Bill Vail to myself and others) are there.

AMB

Well half a loaf is better than none at least I have the MVVS 61 diesel. It should be interesting to see what prop that beast runs
Fiery wil get it sorted out martin

fiery

My Feedback: (2)

Prop? I have a stunning new 16 x 10 Mejzlik which I am saving for it.

If a carbon fibre prop can be called beautiful, Mejzlik is the name.

dennis

My Feedback: (90)

I have a NIB MVVS 1.2 twin that I'll never use and I have one MVVS 61 diesel head. I did run Tartan Twins as a diesel and it involves nothing more then adapting a ST 61 carb to the plate and go from there. Be aware though the twin has an 11.1 compression ratio as a glow ,so care is needed with this set up . You really don't need too much squeeze to get it to light off.
it will astound you with it's performance.
dennis

gmedson

[&:] Um - Dennis, if you will not be using your MVVS 120, would you like to sell it? I am interested in what fiery is doing and would like to experiment myself. Actually, not to be greedy, I would take the .61 diesel head too in order to keep my eyes open for a reasonably priced .61 glow on eBay. For the 1.20 I would make my own diesel heads. I can do that for the .61 too, of course, but a ready-made head would save several hours of shop time. I use essentially Bob Davis' design but my own external style to suit engine.

Fiery - Thanks for the info on the Walbro carb and on the MVVS forum thread. Will you also try using a .60-size rc carbie? Ever so much simpler, I should think. Assuming that one is set up to make an adapter or whole new manifold. That would leave just the reed-valve assembly to optimize thru experiment. Of course I have not had one of these puppies in my hands to get a better idea of what all might be involved...

Thanks Guys. -Gary

fiery

My Feedback: (2)

Hi Gary

I have thought long about just using a standard R/C carb. Pe Reivers suggests this and I listen to what he says.

One big issue if you were to use a standard R/C carb is it's location. It would sit way up on top of the engine. It would make mounting the engine on a standard airframe impossible.

I do not want the carb in an inverted position also. I am sure that is why the MVVS factory opted for Walbro carb, and mounted it on top. I has a diaphragm pump. I like that the Walbro has a built in diaphragm. It will pump fuel up to the carb and keep it there. Fuel head / tank position problem solved. And gravity will flow fuel in the engine, not out.

If I use a standard R/C carb I would need to install a Cline or Iron Bay regulator. Whether these or either of them are suited to diesel fuel I do not know. I also do not want the extra hassle of a separate pump. So, that is option No. 2. For now I will stick with the Walbro (option No. 1) unless I cannot get it to work.

I have scourced a Walbro WT-499. Orientation with the factory hold down position and pressure pulse is an issue. The throttle arm and needles face the wrong way (forward) with this style of Walbro. I may need to work on this to get the Carb oriented correctly for throttle actuation. I do not want a bellcrank involved with throttle operation. I can sort the pressure pulse problem.

fiery

My Feedback: (2)

Gary, factory heads, now a polished "high" finish were less than 25 Euro for the two. Contra fit seems good. The proof will be in the eating of that particular pudding. Unlike some, I have never had a problem with the MVVS diesel head on my ancient MVVS .61 D.

dennis

My Feedback: (90)

While I can't speak about the MVVS I do know that the Tartan twin and single have been run in every position imagionable with a standard ST60 carb with no fuel feed problems. With the compression ratio of these engines and case pressure fuel draw is not a serious problem.

Incidentally the best position for the twin was always the inverted position..If your worried about carb position take a look at the forward facing carb set up that the Tartans used and copy it. Your problems will be simply solved.
Dennis

pe reivers

With all the carbs you have at hand now, why not bash one and using the pump/regulating section only to feed fuel to the standard MVVS carb? Advantage is, that you can apply exhaust pressure to the regulating membrane and have fuel injection at high engine loads. (this system has been tried in glow engines with good results, and is one step ahead of the Cline regulator)

fiery

My Feedback: (2)

Dennis,

What you say is true, many flat twins have updraught carbs.

It is problematic on the MVVS as an updraught carb arrangement interferes with exhaust muffler installation. Throttle actuation also becomes difficult.

Pe,

What you say makes sense. I already have an Iron Bay regulator, which on further consideration I believe would suit. It has an alloy body unlike the Cline, which has a composite housing, and may be adversely affected by petroleum fuels. No need for me to "bash" a Walbro .

I also have a large MVVS carb spare ... you sold me it. 9 mm bore. I am well set up to take that path if I do not achieve success with the Walbro.

pe reivers

I know

I have used walbro pumps/regulators on glow fuel, but found the moving parts prone to hardening with the methanol used. Diesel fuels probably will be much more forgiving.

dennis

My Feedback: (90)

I'm not 100% sure but i believe that Walbro sells conversions for some of their carbs for alcohol. Basically the seals and o rings. However I'm not sure that you can get a new body or needles to handle the increased flow that you need for glow fuel. But they do sell carbs that are made for alky fuels , They are reasonably priced.
Dennis